Carbylamine test is used to detect the presence of primary amino group in an organic compound. Which of the following compound is formed when this test is performed with aniline?

Solution

Chemistry ma’am · 4 steps

Aniline keeps its nitrogen on the ring; chloroform swaps the two N–H hydrogens for one carbon.

1. Make the carbene. Heat the amine with chloroform and alcoholic KOH. The base removes H and Cl from CHCl₃ to give dichlorocarbene, :CCl₂.
2. Build the isocyanide. The lone pair on the amine nitrogen attacks :CCl₂. The two N–H hydrogens then leave with the two chlorines as HCl, which KOH neutralises. This leaves -N≡C, with the ring still bonded to nitrogen.

   C₆H₅NH₂ + CHCl₃ + 3KOH →(Δ) C₆H₅NC + 3KCl + 3H₂O

3. Why only primary. The reaction uses up two H atoms on the same nitrogen, and only a primary amine has two. The product, phenyl isocyanide, has a very foul smell, and that smell is the positive test.
4. So. The product is phenyl isocyanide, C₆H₅-NC, with the ring bonded to N. That is option (d).

The idea to keep. Carbylamine test: RNH₂ + CHCl₃ + 3KOH gives R-NC. The R group stays on nitrogen, and the foul-smelling isocyanide forms only from primary amines.

Answer from the NTA final answer key. Solution by PrepWiser.